In general, persons wishing to contact a particular party initiate a call to a telephone specifically known to be associated with that party, such as the party's office or wireless telephone. A disadvantage of this method of communication is that parties are not always in close proximity to such associated telephones, or for that matter, in close proximity to any telephone. This presents a problem to persons who need to immediately contact a mobile party, regardless of that party's location.
Several technologies have developed in an effort to solve the problem of establishing communication with a mobile party. These include call forwarding, paging, and cellular systems. However, each of these technologies has drawbacks which prevent seamless and ubiquitous communication.
The inventions disclosed in the Ser. No. 08/379,425 and Ser. No. 08/379,430 applications (the '425 and '430 inventions, respectively), cited hereinabove, address many of the problems associated with prior systems used to communicate with mobile individuals. Generally, both of those inventions describe a call routing scheme in which each subscriber is assigned a Personal Telephone Number (PTN) and uses a two-way pager to route calls directed to that number. In the '430 invention, when a call is placed to the subscriber's PTN, a network database query is generated and information about how to handle the call is retrieved (referred to as "registration" type routing). In the '425 invention, when a call is placed to the subscriber's PTN, the subscriber's pager number is retrieved from the database and an alerting page is sent to the subscriber. The subscriber may then use the two-way pager to transmit a terminating number back to the network in response to the alerting page (referred to as "call-by-call" type routing).
Despite the numerous advantages of the '425 and '430 inventions, they do not account for those situations in which a subscriber is unable, or unwilling, to respond to a call-by-call alerting page when that mode of routing is invoked. In such "subscriber unavailable" situations, inadequate call treatment can waste network resources and result in the subscriber missing important calls. For example, consider a situation in which a subscriber goes to work and leaves her two-way pager at home. If the subscriber has specified call-by-call mode and a call is placed to the subscriber's PTN then the network will hold the call, page the subscriber, and await a response. A response, however, will not be provided since the subscriber is unavailable. One way to handle such a situation is to automatically route the call to voice mail following a predetermined "time out" period.
Although a time out procedure provides a method for dealing with the subscriber unavailable problem, the procedure has drawbacks. One drawback of the time out procedure is that it requires that an unnecessary page be sent. Another drawback of the time out procedure is that there exists a possibility that a caller will not continue to hold on the call for the duration of the time out period, in which case the subscriber will "miss" the call.